var.visit

auto visit(handlers...)() const @safe

Apply a visitor pattern to this value, dispatching to the appropriate handler based on type.

This provides type-safe dispatch without manual switch on Type, similar to std.variant.visit. Handlers are provided as template arguments and can be lambdas, function pointers, or delegates.

Handler Selection:

Handlers accepting specific types (bool, long, double, string, var[], var[string]) are matched first.
A handler accepting var serves as a catch-all fallback.
If no matching handler is found for the current type, returns the default value of the return type.

Type Mapping:

NULL: matched by typeof(null) handler or fallback
BOOL: matched by bool handler
Integer types (BYTE..ULONG): matched by long handler (widened)
Floating types (FLOAT, DOUBLE, REAL): matched by double handler (widened)
STRING: matched by string handler
ARRAY: matched by var[] handler
OBJECT: matched by var[string] handler
Character types (CHAR, WCHAR, DCHAR): matched by dchar handler (widened)

Parameters

handlers One or more callable handlers for different types.

Returns

The result of calling the matched handler, or R.init if no handler matches.

Examples

var v = 42;
string result = v.visit!(
  (long n) => "integer: " ~ n.to!string,
  (string s) => "string: " ~ s,
  (var fallback) => "other: " ~ fallback.toString()
);
assert(result == "integer: 42");

var s = "hello";
auto r = s.visit!(
  (long n) => n * 2,
  (string str) => cast(long)str.length
);
assert(r == 5); // length of "hello"